This invention relates to method and apparatus for face seaming carpet pieces with hot melt adhesive tapes.
This invention relates particularly to an iron which forms a raised center bead of adhesive in the molten hot melt adhesive produced at the outlet end of the iron. The raised center bead coats the side edges of the carpet backings with hot melt adhesive. These edges are locked directly together by the interposed hot melt adhesive after the adhesive cools to a solid condition.
For many years a hot melt adhesive carpet seaming tape and a face seaming process (with the hot melt adhesive activated by an iron placed on the tape and under the pieces of carpet to be joined) have been the most widely used tape and seaming methods for joining pieces of carpet.
While seams made this way are very good in a majority of the installations, a certain number of seams will peak and others will have flex failures.
Peaking results from the seam being elevated slightly when the carpet is stretched into place, making the whole seam visible from the top of the carpet.
Flex failures are a splitting of the tape directly under the line where the two pieces of carpet meet. Flex failures usually occur when very stiff carpet is applied over soft, thick underlayment. Flex failures are particularly likely to occur when bundles of glass fibers are used as the strength members for reinforcement of the tape. If the bundles of glass fibers are not sufficiently well encapsulated and held in place by the hot melt adhesive, the bundles can become exposed and the glass fibers can then cut one another; because glass fibers do not chafe well.
Another problem which has occurred in seams made by prior art hot melt adhesive tape face seaming techniques is raveling out of the tufts at the seam. This happens because the carpet pieces, when cut to make the seam, may permit some of the tufts immediately adjacent the cut to become loose enough to ravel out. When a carpet piece is cut, there can be a loss of locking of the strands in the carpet backing which are nearest the cut. The tufts or yarn can then strip out, because there is nothing to hold the yarn there. This raveling problem can still be present after the carpet has been seamed with the usual face seaming process, because the hot melt adhesive on the underside of the carpet backing does not replace the continuity of the uncut carpet backing on the cut edge. The conventional face seaming processes with hot melt adhesive are usually not effective to get adhesive up into the space between the edges of the carpet backing for locking the loose tufts in place.
Another problem which has been present in seams produced by prior art hot melt seaming techniques has been the problem of separation of the secondary backing from the primary backing. In some carpets the tufts are attached to a primary backing, and the primary backing is glued to a secondary backing. When pieces of carpet having such primary and secondary backings are cut (as part of making a seam), the primary backing can become separated from the secondary backing. Such separation can make the seam visible.
Carpet manufacturers have recommended putting latex along the edges of all cut carpet edges before hot melt face seaming, but virtually no layers use the procedure. The procedure requires considerable time. The time required to do the latex sealing is often longer than the time required to do a face seam itself. Also, latexing the carpet edges is a critical operation. If the latex is put in the wrong place, the hot melt adhesive will not bond to the latex.